Method and apparatus for multipath demodulation in a code division multiple access communication system

ABSTRACT

Multipath RAKE receiver structure that allows for the concurrent demodulation of multipath signals that arrive at the receiver at arbitrarily low arrival time differences. The fingers are set to be a fixed offset from one another. One finger tracks the shift in the peak of the multipath component and the additional fixed offset fingers follow the tracking.

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention relates to communications. More particularly, thepresent invention relates to a novel and improved method and apparatusfor demodulating code division multiple access (CDMA) signals.

II. Description of the Related Art

In a wireless radiotelephone communication system, many userscommunicate over a wireless channel to connect to wireline telephonesystems. Communication over the wireless channel can be one of a varietyof multiple access techniques that allow a large number of users in alimited frequency spectrum. These multiple access techniques includetime division multiple access (TDMA), frequency division multiple access(FDMA), and code division multiple access (CDMA).

The CDMA technique has many advantages. An exemplary CDMA system isdescribed in U.S. Pat. No. 4,901,307, entitled “SPREAD SPECTRUM MULTIPLEACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS”,assigned to the assignee of the present invention and incorporated byreference herein.

In the '307 patent, a multiple access technique is disclosed where alarge number of mobile telephone system users, each having atransceiver, communicate through satellite repeaters or terrestrial basestations using CDMA spread spectrum communication signals. The basestation-to-mobile station signal transmission path is referred to as theforward link and the mobile station-to-base station signal transmissionpath is referred to as the reverse link.

In using CDMA communications, the frequency spectrum can be reusedmultiple times thus permitting an increase in system user capacity. Eachbase station provides coverage to a limited geographic area and linksthe mobile stations in its coverage area through a cellular systemswitch to the public switched telephone network (PSTN). When a mobilestation moves to the coverage area of a new base station, the routing ofthat user's call is transferred to the new base station.

The CDMA modulation techniques discussed in the '307 patent and in U.S.Pat. No. 5,102,459 entitled “SYSTEM AND METHOD FOR GENERATING SIGNALWAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM”, assigned to the assigneeof the present invention and incorporated by reference herein, mitigatethe special problems of the terrestrial channel, such as multipath andfading. Instead of being an impediment to system performance, as it iswith narrowband systems, separable multipaths can be diversity combinedin a mobile rake receiver for enhanced modem performance. The use of aRAKE receiver for improved reception of CDMA signals is disclosed inU.S. Pat. No. 5,109,390, entitled “DIVERSITY RECEIVER IN A CDMA CELLULARTELEPHONE SYSTEM”, assigned to the assignee of the present invention andincorporated by reference herein. In the mobile radio channel, multipathis created by reflection of the signal from obstacles in theenvironment, such as buildings, trees, cars, and people. In general themobile radio channel is a time varying multipath channel due to therelative motion of the structures that create the multipath. Forexample, if an ideal impulse is transmitted over the time varyingmultipath channel, the received stream of pulses would change in timelocation, attenuation, and phase as a function of the time that theideal impulse was transmitted.

The multipath properties of the terrestrial channel produce, at thereceiver, signals having traveled several distinct propagation paths.One characteristic of a multipath channel is the time spread introducedin a signal that is transmitted through the channel. As described in the'390 patent, the spread spectrum pseudonoise (PN) modulation used in aCDMA system allows different propagation paths of the same signal to bedistinguished and combined, provided the difference in path delaysexceeds the PN chip duration. If a PN chip rate of approximately 1 MHzis used in a CDMA system, the full spread spectrum processing gain,equal to the ratio of the spread bandwidth to the system data rate, canbe employed against paths having delays that differ by more than onemicrosecond. A one microsecond path delay differential corresponds to adifferential path distance of approximately 300 meters.

Another characteristic of the multipath channel is that each paththrough the channel may cause a different attenuation factor. Forexample, if an ideal impulse is transmitted over a multipath channel,each pulse of the received stream of pulses generally has a differentsignal strength than other received pulses.

Yet another characteristic of the multipath channel is that each paththrough the channel may cause a different phase on the signal. If, forexample, an ideal impulse is transmitted over a multipath channel, eachpulse of the received stream of pulses generally has a different phasethan other received pulses. This can result in signal fading.

A fade occurs when multipath vectors are added destructively, yielding areceived signal that is smaller than either individual vector. Forexample, if a sine wave is transmitted through a multipath channelhaving two paths where the first path has an attenuation factor of X dB,a time delay of d with a phase shift of Q radians, and the second pathhas an attenuation factor of X dB, a time delay of d with a phase shiftof Q+π radians, no signal would be received at the output of thechannel.

As described above, in current CDMA demodulator structures, the PN chipinterval defines the minimum separation two paths must have in order tobe combined. Before the distinct paths can be demodulated, the relativearrival times (or offsets) of the paths in the received signal mustfirst be determined. The demodulator performs this function by“searching” through a sequence of offsets and measuring the energyreceived at each offset. If the energy associated with a potentialoffset exceeds a certain threshold, a demodulation element, or “finger”may be assigned to that offset. The signal present at that path offsetcan then be summed with the contributions of other fingers at theirrespective offsets.

A method and apparatus of finger assignment based on searcher and fingerenergy levels is disclosed in U.S. Pat. No. 5,490,165, entitled “FINGERASSIGNMENT IN A SYSTEM CAPABLE OF RECEIVING MULTIPLE SIGNALS”, assignedto the assignee of the present invention and incorporated by referenceherein. In the exemplary embodiment, the CDMA signals are transmitted inaccordance with the Telecommunications Industry AssociationTIA/EIA/IS-95-A, entitled “MOBILE STATION-BASE STATION COMPATIBILITYSTANDARD FOR DUAL-MODE WIDEBAND SPREAD SPECTRUM CELLULAR SYSTEM”. Anexemplary embodiment of the circuitry capable of demodulating IS-95forward link signals is described in detail in U.S. Pat. No. 5,764,592,entitled “MOBILE DEMODULATOR ARCHITECTURE FOR A SPREAD SPECTRUM MULTIPLEACCESS SYSTEM”, assigned to the assignee of the present invention andincorporated by reference herein. An exemplary embodiment of thecircuitry capable of demodulating IS-95 reverse link signals isdescribed in detail in U.S. Pat. No. 5,654,979, entitled “CELL SITEDEMODULATOR ARCHITECTURE FOR A SPREAD SPECTRUM MULTIPLE ACCESSCOMMUNICATION SYSTEM,” assigned to the assignee of the present inventionand incorporated by reference herein.

FIG. 1 shows an exemplary set of signals from a base station arriving atthe mobile station. It will be understood by one skilled in the art thatFIG. 1 is equally applicable to the signals from a mobile stationarriving at the base station. The vertical axis represents the powerreceived on a decibel (dB) scale. The horizontal axis represents thedelay in the arrival time of a signal due to multipath delays. The axis(not shown) going into the page represents a segment of time. Thesignals in the common plane traveled along different paths arriving atthe receiver at the same time, but having been transmitted at differenttimes.

In a common plane, peaks to the right were transmitted at an earliertime by the base station than peaks to the left. For example, theleft-most peak spike 2 corresponds to the most recently transmittedsignal. Each signal spike 2-7 has traveled a different path andtherefore exhibits a different time delay and a different amplituderesponse.

The six different signal spikes represented by spikes 2-7 arerepresentative of a severe multipath environment. Typical urbanenvironments produce fewer usable paths. The noise floor of the systemis represented by the peaks and dips having lower energy levels.

The task of the searcher is to identify the delay as measured by thehorizontal axis of signal spikes 2-7 for potential finger assignment.The task of the finger is to demodulate one of a set of the multipathpeaks for combination into a single output. It is also the task of afinger, once assigned to a multipath peak, to track that peak as it maymove in time.

The horizontal axis can also be thought of as having units of PN offset.At any given time, the mobile station receives a variety of signals froma base station, each of which has traveled a different path and may havea different delay than the others. The base station's signal ismodulated by a PN sequence. A local copy of the PN sequence is alsogenerated at the mobile station. Also at the mobile station, eachmultipath signal is individually demodulated with a PN sequence codealigned to its received time offset. The horizontal axis coordinates canbe thought of as corresponding to the PN sequence code offset that wouldbe used to demodulate a signal at that coordinate.

Note that each of the multipath peaks varies in amplitude as a functionof time, as shown by the uneven ridge of each multipath peak. In thelimited time shown, there are no major changes in the multipath peaks.Over a more extended time range, multipath peaks disappear and new pathsare created as time progresses. The peaks can also slide to earlier orlater offsets as the path distances change when the mobile station movesrelative to the base station. Each finger tracks these small variationsin the signal assigned to it.

In narrowband systems, the existence of multipath in the radio channelcan result in severe fading across the narrow frequency band being used.Such systems are capacity constrained by the extra transmit power neededto overcome a deep fade. As noted above, CDMA signal paths may bediscriminated and diversity combined in the demodulation process.

Three major types of diversity exist: time diversity, frequencydiversity, and space/path diversity. Time diversity can best be obtainedby the use of repetition, time interleaving, and error correction anddetection coding that introduce redundancy. A system may employ each ofthese techniques as a form of time diversity.

CDMA, by its inherent wideband nature, offers a form of frequencydiversity by spreading the signal energy over a wide bandwidth. Thefrequency selective fading that can cause a deep fade across anarrowband system's frequency bandwidth usually only affects a fractionof the frequency band employed by the CDMA spread spectrum signal.

The rake receiver provides path diversity through its ability to combinemultipath delayed signals; all paths that have a finger assigned to themmust fade together before the combined signal is degraded. Additionalpath diversity is obtained through a process known as “soft hand-off” inwhich multiple simultaneous, redundant links from two or more basestations can be established with the mobile station. This supports arobust link in the challenging environment at the cell boundary region.Examples of path diversity are illustrated in U.S. Pat. No. 5,101,501entitled “SOFT HAND-OFF IN A CDMA CELLULAR TELEPHONE SYSTEM”, and U.S.Pat. No. 5,109,390 entitled “DIVERSITY RECEIVER IN A CDMA CELLULARTELEPHONE SYSTEM”, both assigned to the assignee of the presentinvention and incorporated by reference herein.

Both the cross-correlation between different PN sequences and theautocorrelation of a PN sequence, for all time shifts other than zero,have a nearly zero average value. This allows the different signals tobe discriminated upon reception. Autocorrelation and cross-correlationrequire that logical “0” take on a value of “1” and logical “1” take ona value of “−1”, or a similar mapping, in order that a zero averagevalue be obtained.

However, such PN signals are not orthogonal. Although thecross-correlation essentially averages to zero over the entire sequencelength for a short time interval, such as an information bit time, thecross-correlation is a random variable with a binomial distribution. Assuch, the signals interfere with each other in much the same manner asif they were wide bandwidth Gaussian noise at the same power spectraldensity.

It is well known in the art that a set of n orthogonal binary sequences,each of length n, for n any power of 2 can be constructed (see DigitalCommunications with Space Applications, S. W. Golomb et al.,Prentice-Hall, Inc., 1964, pp. 45-64). In fact, orthogonal binarysequence sets are also known for most lengths that are multiples of fourand less than two hundred. One class of such sequences that is easy togenerate is called the Walsh function; a Walsh function of order n canbe defined recursively as follows: $\begin{matrix}{{W(n)} = {\begin{matrix}{W\left( \frac{n}{2} \right)} & {W\left( \frac{n}{2} \right)} \\{W\left( \frac{n}{2} \right)} & {W\left( \frac{n}{2} \right)}\end{matrix}}} & (1)\end{matrix}$

where W′ denotes the logical complement of W, and W(0)=|0|.

A Walsh sequence or code is one of the rows of a Walsh function matrix.A Walsh function matrix of order n contains n sequences, each of lengthn Walsh chips. A Walsh function matrix of order n (as well as otherorthogonal functions of length n) has the property that over theinterval of n bits, the cross-correlation between all the differentsequences within the set is zero. Every sequence in the set differs fromevery other sequence in exactly half of its bits. It should also benoted that there is always one sequence containing all zeroes and thatall the other sequences contain half ones and half zeroes.

In the system described in the '459 patent, the call signal begins as a9600 bit per second information source which is then converted by a rate1/2 forward error correction encoder to a 19,200 symbols per secondoutput stream. Each call signal broadcast from a cell is covered withone of sixty-four orthogonal Walsh sequences, each sixty-four Walshchips, or one symbol, in duration. Regardless of the symbol beingcovered, the orthogonality of all Walsh sequences ensures that allinterference from other user signals in that cell are canceled outduring symbol integration. The non-orthogonal interference from othercells limits capacity on the forward link.

Each base station in a CDMA system transmits in the same frequency bandusing the same PN sequence, but with a unique offset relative to anunshifted PN sequence aligned to a universal time reference. The PNspreading rate is the same as the Walsh cover rate, 1.2288 MHz, or 64 PNchips per symbol. In the preferred embodiment, each base stationtransmits a pilot reference. In the description of the present inventiondifferent information is transmitted on the I and Q channels whichincreases the capacity of the system.

The pilot channel is a “beacon” transmitting a constant zero symbol andspread with the same I and Q PN sequences used by the traffic bearingsignals. In the exemplary embodiment, the pilot channel is covered withthe all zero Walsh sequence 0. During initial system acquisition themobile searches all possible shifts of the PN sequence and once it hasfound a base station's pilot, it can then synchronize itself to systemtime. As detailed below, the pilot plays a fundamental role in themobile demodulator rake receiver architecture well beyond its use ininitial synchronization.

FIG. 2 depicts a generic rake receiver demodulator 10 for receiving anddemodulating the forward link signal 20 arriving at the antenna 18. Theanalog transmitter and receiver 16 contain a QPSK downconverter chainthat outputs digitized I and Q channel samples 32 at baseband. Thesampling clock, CHIPX8 40, used to digitize the receive waveform, isderived from a voltage controlled temperature compensated localoscillator (TCXO).

The demodulator 10 is supervised by a microprocessor 30 through thedatabus 34. Within the demodulator, the I and Q samples 32 are providedto a plurality of fingers 12 a-c and a searcher 14. The searcher 14searches out windows of offsets likely to contain multipath signal peakssuitable for assignment of fingers 12 a-c. For each offset in the searchwindow, the searcher 14 reports the pilot energy it found at that offsetto the microprocessor. The fingers 12 a-c are then surveyed, and thoseunassigned or tracking weaker paths are assigned by the microprocessor30 to offsets containing stronger paths identified by searcher 14.

Once a finger 12 a-c has locked onto the multipath signal at itsassigned offset it then tracks that path on its own until the path fadesaway or until it is reassigned using its internal time tracking loop.This finger time tracking loop measures energy on either side of thepeak at the offset at which the finger is currently demodulating. Thedifference between these energies forms a metric which is then filteredand integrated.

The output of the integrator controls a decimator that selects one ofthe input samples over a chip interval to use in demodulation. If a peakmoves, the finger adjusts its decimator position to move with it. Thedecimated sample stream is then despread with the PN sequence consistentwith the offset to which the finger is assigned. The despread I and Qsamples are summed over a symbol to produce a pilot vector (P_(I),P_(Q)). These same despread I and Q samples are Walsh uncovered usingthe Walsh code assignment unique to the mobile user and the uncovered,despread I and Q samples are summed over a symbol to produce a symboldata vector (D_(I), D_(Q)). The dot product operator is defined as

P(n)·D(n)=P _(I)(n)D _(I)(n)+P _(Q)(n)D _(Q)(n),  (2)

where P_(I)(n) and P_(Q)(n) are respectively the I and Q components ofthe pilot vector P for symbol n and D_(I)(n) and D_(Q)(n) arerespectively the I and Q components of the data vector D for symbol n.

Since the pilot signal vector is much stronger than the data signalvector it can be used as an accurate phase reference for coherentdemodulation; the dot product computes the magnitude of the data vectorcomponent in phase with the pilot vector. As described in U.S. Pat. No.5,506,865, entitled “PILOT CARRIER DOT PRODUCT CIRCUIT” and assigned tothe assignee of the present invention and incorporated by referenceherein, the dot product weights the finger contributions for efficientcombining, in effect scaling each finger symbol output 42 a-c by therelative strength of the pilot being received by that finger. Thus thedot product performs the dual role of both phase projection and fingersymbol weighting needed in a coherent rake receiver demodulator.

Each finger has a lock detector circuit that masks the symbol output tothe combiner 42 if its long term average energy does not exceed aminimum threshold. This ensures that only fingers tracking a reliablepath will contribute to the combined output, thus enhancing demodulatorperformance.

Due to the relative difference in arrival times of the paths to whicheach finger 12 a-c is assigned, each finger 12 a-c has a deskew bufferthat aligns the finger symbol streams 42 a-c so that the symbol combiner22 can sum them together to produce a “soft decision” demodulatedsymbol. This symbol is weighted by the confidence that it correctlyidentifies the originally transmitted symbol. The symbols are sent to adeinterleaver/decoder circuit 28 that first frame deinterleaves and thenforward error correction decodes the symbol stream using the maximumlikelihood Viterbi algorithm. The decoded data is then made available tothe microprocessor 30 or to other components, such as a speech vocoder,for further processing.

To demodulate correctly, a mechanism is needed to align the localoscillator frequency with the clock used at the cell to modulate thedata. Each finger makes an estimate of the frequency error by measuringthe rotation rate of the pilot vector in QPSK I, Q space using the crossproduct vector operator:

P(n)×P(n−1)=P _(I)(n)P _(Q)(n−1)−P _(I)(n−1)P _(Q)(n)  (3)

The frequency error estimates from each finger 44 a-c are combined andintegrated in frequency error combiner 26. The integrator output, LO_ADJ36, is then fed to the voltage control of the TCXO in the analogtransmitter and receiver 16 to adjust the clock frequency of the CHIPX8clock 40, thus providing a closed loop mechanism for compensating forthe frequency error of the local oscillator.

As described above, in current demodulator structures, a path mustdiffer by at least one PN chip to have a separate finger allocated toits demodulation. However, there are cases when paths differ by lessthan a PN chip interval in the time, this situation leads to theexistence of a “fat path”. Under traditional demodulatorimplementations, only one finger could be allocated to demodulate thefat path. One of the reasons for this is that once assigned to a path,the finger tracks the path movement independently. Without centralcoordination of the fingers multiple fingers will converge to the samepeak of the fat path. In addition, the searcher tends to get confusedwhen paths are tracked which are to close to one another

On an orthogonal forward link, there is a great deal of energy in eachof the paths because all of the energy from the base station to allmobiles is transmitted using the same PN offset which are channelized byuse of orthogonal code sequences. Moreover, orthogonal code sequenceshave poor autocorrelation in that the correlation between orthogonalcode sequences is high. Thus, when paths on the forward link differ byless than a PN chip interval, the signals cannot be distinguished fromone another by the outer PN spreading nor is the coding gain of theorthogonal spreading realized because of the time shift. The energy ofthe close multipath components in this case serves as noise andsubstantially degrades the performance of the demodulator assigned tothe fat path. On the reverse link, close multipath components can alsocause degradation of the demodulator assigned to the fat path.

The present invention is described with respect to the improvement ofthe demodulation of the forward link. However, the present invention isequally applicable to improving the demodulation of the reverse link.

SUMMARY OF THE INVENTION

The present invention is a novel and improved method and apparatus formultipath demodulation in a code division multiple access communicationsystem. In current demodulator architectures, an accumulator is providedfor each finger and the combining operation is performed subsequent tothe accumulation operation. In the present invention, a demodulatorstructure is described that reduces the amount of hardware and softwarein the receiver by reducing the number of symbol accumulators to one.

Moreover, the present invention describes a demodulator structure thatallows for the concurrent demodulation of multipath signals that arriveat the receiver at arbitrarily low arrival time differences. Asdescribed above, traditional demodulator structures prohibit theassignment of arbitrarily close fingers because the fingers converge tothe peak of the path, negating any possible benefit sought fromassigning the fingers to paths that are very close. In the presentinvention, the fingers are set to be a fixed offset from one another. Inthe present invention, one finger tracks the shift in the peak of themultipath component and the additional fixed offset fingers follow thetracking.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, objects, and advantages of the present invention willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout and wherein:

FIG. 1 represents an exemplary severe multipath signal condition;

FIG. 2 is a block diagram of a current demodulation system;

FIG. 3 is an illustration of a fat path situation in which a number ofmultipath components are very closely spaced with respect to one anotherin arrival times at the receiver;

FIG. 4 is an illustration of the receiver structure that provides foreffective demodulation of the closely spaced multipath components;

FIG. 5 is an illustration of an improved demodulation structure thatallows for a single accumulator in the receiver architecture;

FIG. 6 is a first embodiment of the fat path demodulator of the presentinvention wherein four fingers are used to demodulate four multipathcomponents with arrival times offset from one another by half of one PNchip wherein the method of path discrimination is through the offsettingof the PN sequences with accompanying deskewing prior to combination;

FIG. 7 is a second embodiment of the fat path demodulator of the presentinvention wherein four fingers are used to demodulate four multipathcomponents with arrival times offset from one another by half of one PNchip wherein the received signal is delayed by varying amounts of timesbefore being provided to the respective fingers;

FIG. 8 is a third embodiment of the fat path demodulator of the presentinvention wherein six fingers are used to demodulate six multipathcomponents with arrival times offset from one another by half of one PNchip wherein the received signal is delayed by varying amounts of timesbefore being provided to the respective fingers;

FIG. 9 is a fourth embodiment of the fat path demodulator of the presentinvention wherein five fingers are used to demodulate five multipathcomponents with arrival times offset from one another by one third ofone PN chip wherein the received signal is delayed by varying amounts oftimes before being provided to the respective fingers;

FIG. 10 illustrates an alternative embodiment that allows forelimination of the input switch;

FIG. 11 illustrates an alternative embodiment that allows foreleimination of all but one Walsh sequence multiplier;

FIG. 12 illustrates an alternative embodiment that allows for theelimination of two demodulator structures; and

FIG. 13 illustrates an alternative embodiment that allows for theelimination of two demodulators and allows the reciver to operate at thePN chip rate

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3 shows an exemplary set of signals from a base station arriving atthe mobile station at a given time. It will be understood by one skilledin the art that FIG. 3 is equally applicable to the signals from amobile station arriving at the base station. The vertical axisrepresents the power received on a decibel (dB) scale. The horizontalaxis represents the delay in the arrival time of a signal due tomultipath delays. The signals on the x-axis traveled along differentpaths arriving at the receiver at the same time, but having beentransmitted at different times.

In a common plane, peaks to the right were transmitted at an earliertime by the base station than peaks to the left. For example, theleft-most peak spike 50 corresponds to the most recently transmittedsignal. Each signal spike 50, 54 and 58 has traveled a different pathand therefore exhibits a different time delay and a different amplituderesponse.

The three different signal spikes represented by spikes 50, 54 and 58are representative of a severe multipath environment. As describedpreviously, the task of the searcher is to identify the delay asmeasured by the horizontal axis of signal spikes 50, 54 and 58 forpotential finger assignment. However, in the present invention, theadditional task of the searcher is to identify peak 54 as a fat path orset of multipath components to which the demodulator structure of thepresent invention is capable of effective demodulation of closemultipath components. The task of each of the finger is to demodulateone of a set of the multipath peaks for combination into a singleoutput. It is also the task of a finger, once assigned to a multipathpeak, to track that peak as it may move in time.

FIG. 4 depicts the rake receiver demodulator 110 of the presentinvention for receiving and demodulating the forward link signal 120arriving at the antenna 118 of the present invention. The analogtransmitter and receiver 116 contain a QPSK downconverter chain thatoutputs digitized I and Q channel samples 132 at baseband. In anexemplary embodiment, the sampling clock, CHIPX8 140, used to digitizethe receive waveform, is derived from a voltage controlled temperaturecompensated local oscillator (TCXO).

The demodulator 110 is supervised by a microprocessor 130 through thedatabus 134. Within the demodulator, the I and Q samples 132 areprovided to a plurality of fingers 112 a-c and a searcher 114. Althoughthe exemplary embodiment is described in terms of QPSK demodulation, thepresent invention is equally applicable to BPSK, QAM (QuadratureAmplitude Modulation), M-ary PSK or any known modulation method. Thesearcher 114 searches out windows of offsets likely to contain multipathsignal peaks suitable for assignment of fingers 112 a-c. For each offsetin the search window, the searcher 114 reports the pilot energy it foundat that window of offsets to the microprocessor 130. In the presentinvention, microprocessor 130 determines where to assign fingers anddetermines whether and where to assign a fat path demodulators.

Searcher 114 reports the energies in a window around peaks 50, 54 and58. Microprocessor 130 determine from the reported energies that peaks50 and 58 were narrow and could be successfully demodulated with asingle path demodulator. Microprocessor 130 would also be able toidentify the multipath component at peak 54 as a fat path and wouldassign for its demodulation the fat path demodulator of the presentinvention. So for example, fingers 112 a and 112 b demodulate singlepaths and are assigned to paths 50 and 58 of FIG. 3. Finger 112 c, onthe other hand, are directed by microprocessor 130 to perform a fat pathdemodulation and would be assigned to demodulate path 54.

FIG. 5 illustrates a novel RAKE receiver structure that uses a singleaccumulator instead of an accumulator for.each finger as is provided incurrent RAKE receiver structures. The digitized samples are provided tocomplex PN despreader 150 of demodulator 158. In the exemplaryembodiment, the signals are complex PN spread as described in U.S.patent application Ser. No. 08/856,428, entitled “HIGH DATA RATE CDMAWIRELESS COMMUNICATION SYSTEM USING VARIABLE SIZED CHANNEL CODES,” filedMay 14, 1997, assigned to the assignee of the present invention andincorporated by reference herein, in accordance with the followingequations:

I=I′PN _(I) +Q′PN _(Q)  (4)

Q=I′PN _(Q) −Q′PN _(I).  (5)

where PN_(I) and PN_(Q) are distinct PN spreading codes and I′ and Q′are two channels being spread at the transmitter. Complex PN despreader150 removes the complex spreading based on the PN codes, PN_(I) andPN_(Q), to provide two complex PN despread signals.

The complex PN despread signals are provided to pilot filter 152 andcomplex conjugate multiplier 154. Pilot filter 152 uncovers the pilotsignal in accordance with the orthogonal covering (W_(pilot)) and, in apreferred embodiment, provides some filtering to the resultant signal toremove the effects of noise on the received signal. In the exemplaryembodiment, the pilot signal is covered using Walsh 0 which is the allzeroes Walsh sequence. Thus, uncovering the Walsh sequence is a no opand pilot filter 152 simply acts as a low pass filter to reduce theeffect of channel noise.

Complex conjugate multiplier 154 multiplies the signal from complex PNdespreader 150 by the conjugate of the filtered pilot signal from pilotfilter 152. By multiplying the complex despread data by the conjugate ofthe signals from pilot filter 152, the demodulator removes any phaseerror from the received signal. In effect complex conjugate multiplycircuit projects the received signal onto the pilot signal and outputsthe magnitudes of the projections.

The signals from complex conjugate multiplier 154 are provided to Walshmultiplier 156. Walsh multiplier 156 multiply the I and Q trafficchannels with the orthogonal traffic channel covering sequencesW_(traffic). The traffic channel data is then output to symbol combiner160. Demodulators 158 b and 158 c demodulate the received signals fordifferent multipath components using different PN offsets of PN_(I) andPN_(Q) and are deskewed prior to being provided to combiner 160. In theexemplary embodiment, only signals with energies exceeding apredetermined threshold are combined in combiner 160. The combinedsymbol energies are thereafter provided to accumulator 162 whichaccumulates the combined energy valves over Walsh sequence intervals toprovided estimates of the I+Q values.

In an alternative embodiment, complex conjugate multiplier 154 and Walshmultiplier 156 can be interchanged without the need for altering anyother functions. It will be understood by one skilled in the art thatthe simple rearrangements of elements are well known in the art and arewithin the scope of the present invention.

Before turning our attention to the implementation of the fat fingerdemodulator structure, let us briefly examine the process that allowscombining of the received signals in a CDMA communication system.Referring back to FIG. 1, it was described earlier that the peaks on thecommon plane were transmitted at different times and followed differentpropagation paths so as to arrive at the receiver at a common time. Asdescribed above, the signal in peak 2 corresponds to the most recentlytransmitted signal. The signal in peak 3 was transmitted approximately 2PN chip intervals in time later. In order to combine the information inpeak 2 with the information in peak 3, the information from peak 2 mustbe delayed by two PN chip intervals before being combined with theinformation from peak 3 so that different version of the sameinformation are combined.

The proposed fat path demodulators take advantage of both PN shiftingand time delay to provide for deskewing of the information. Turning toFIG. 6, a fat path demodulator is illustrated which performsdemodulation of fat paths comprising a set of closely spaced multipathcomponents with energy spread across a plurality of PN chips. In FIG. 6,four demodulators 200 a-200 d are provided to demodulate paths that area fixed half PN chip distance from one another. The demodulators movetogether demodulating a PN offsets that are offset from one another byfixed increments. In an alternative embodiment, the microprocessor inthe receiver could be used to determine the shape of the fat path andwould adjust the values of delay elements in accordance with the shapeof the path grouping. In the exemplary embodiment, one of thedemodulators is the master and tracks the peak of set of multipathsignals and the other demodulators act as slaves and follow the trackingof the master demodulator.

Demodulator 200 a and demodulator 200 c demodulate the received signalusing PN sequences that are offset from one another by one PN chipinterval. This can be seen by observing that the signal provided toinput 198 is provided directly to demodulators 200 a and 200 c.Demodulator 200 a demodulates the received signal in accordance with aPN offset from PN generator 206 that is delayed by one PN chip intervalby delay element 208 and in accordance with a Walsh sequence from Walshgenerator 218 that is delayed by one PN chip interval by delay element216.

As described with respect to FIG. 1, the signal demodulated bydemodulator 200 a followed a propagation path that took one PN chiplonger to traverse than the propagation path upon which the signaldemodulated by demodulator 200 c followed. In order to properly combinethe information, delay element 220 delays the data demodulated bydemodulator 200 c prior to combining with the demodulated data fromdemodulator 200 a.

The same combining operation is performed with respect to the signalsdemodulated by demodulators 200 b and 200 d. Demodulators 200 b and 200d demodulate signal that have traversed paths that differ by one half PNchip interval from the signals demodulated by demodulators 200 a and 200c, respectively. The deskewing of the half chip path difference is notperformed by a delays but rather is inherent in the performance of thesignal combining operation in combiner element 224 which combines whenthe demodulated data from demodulators 200 b and 200 d is available tocombiner element 224. This intrinsically means that the information fromdemodulators 200 a and 200 c was provided a half PN cycle earlier thanthe demodulated information from demodulators 200 b and 200 d in essenceperforming the additional deskewing operation. One skilled in the artwill recognize that this operation could be performed by placingaddition ½ PN chip delays on the outputs of demodulators 200 b and 200d.

Moving to the detailed operation of the demodulator of FIG. 6, basebandsamples at twice the PN chip rate are provided to switch 202. Switch 202switches between outputs 198 and 199 at twice the rate of the PN chipcycle. The first base band sample is provided to demodulators 200 a and200 c. The next baseband sample that arrives one half PN chip intervallater is provided to demodulators 200 b and 200 d.

The first sample is provided through switch 202 on line 198 todemodulator 200 a. The sample is PN descrambled in PN descramblingelement 204 a. In the exemplary embodiment, PN descrambling element 204a descrambles the sample in accordance with two PN sequences (PN_(I) andPN_(Q)) provided by PN generator 206. The PN sequences are delayed bydelay element 208 by one PN chip period. The complex despreadingoperation is performed as described above with respect to complexdespreading element 150 of FIG. 5.

The complex PN descrambled sequences are provided to a first input ofcomplex conjugate multiplier 212 a and to pilot filter 210 a. Complexconjugate multiplier removes phase ambiguities that are introduced bythe propagation path. Pilot filter 210 a uncovers the pilot channel inaccordance with the Walsh covering for the pilot channel W_(pilot). Inthe exemplary embodiment, W_(pilot) is the all zeroes Walsh sequence forwhich the uncovering operation is a No Op. In this special case, pilotfilter 210 a is simply a low pass filter which the noise from the pilotsignal. The complex conjugate of the filtered pilot signal and thecomplex PN despread sequences are multiplied in complex conjugatemultiplier 212 a which computes the dot product of the pilot channel andthe PN descrambled sequence to provide a scalar sequence to Walshsequence multiplier 214 a.

Walsh sequence multiplier 214 a multiplies the input scalar sequencefrom complex conjugate multiplier 212 a by the traffic channel Walshsequence from Walsh generator 218 which is delayed by one PN chipinterval by delay element 216. The multiplied sequence is then providedto combiner element 224.

The first sample is redundantly provided through switch 202 on line 198to demodulator 200 c. The sample is PN descrambled in PN descramblingelement 204 c. In the exemplary embodiment, PN descrambling element 204c descrambles the sample in accordance with two PN sequences (PN_(I) andPN_(Q)) provided by PN generator 206. The PN sequences are provideddirectly to PN descrambling element 204c which results in the samplebeing demodulated by a PN sequence offset from the sequence used bydemodulator 200 a by one PN chip interval.

The complex PN descrambled sequences are provided to a first input ofcomplex conjugate multiplier 212 c and to pilot filter 210 c. Pilotfilter 210 c uncovers the pilot channel in accordance with the Walshcovering for the pilot channel W_(pilot). In the exemplary embodiment,W_(pilot) is the all zeroes Walsh sequence for which the uncoveringoperation is a No Op. In this special case, pilot filter 210 c is simplya low pass filter which removes the noise from the pilot signal. Thecomplex conjugate of the filtered pilot signal and the complex PNdespread sequences are multiplied in complex conjugate multiplier 212 cwhich computes the dot product of the pilot channel and the PNdescrambled sequence to provide a scalar sequence to Walsh sequencemultiplier 214 c.

Walsh sequence multiplier 214 c multiplies the input scalar sequencefrom complex conjugate multiplier 212 c by the traffic channel Walshsequence from Walsh generator 218. The multiplied sequence is thenprovided to summing means 224.

After one half PN chip interval, switch 202 toggles so as to put thenext sample, received one half PN chip interval later, on input line 199to demodulators 200 b and 200 d. Within demodulator 200 b, the sample isPN descrambled in PN descrambling element 204 b. As described previouslyPN descrambling element 204 b descrambles the sample in accordance withtwo PN sequences (PN_(I) and PN_(Q)) provided by PN generator 206 b. ThePN sequences are delayed by delay element 208 by one PN chip period.

The complex PN descrambled sequences are provided to a first input ofcomplex conjugate multiplier 212 b and to pilot filter 210 b. Pilotfilter 210 b uncovers the pilot channel in accordance with the Walshcovering for the pilot channel W_(pilot). In the exemplary embodiment,pilot filter 210 b is simply a low pass filter which removes the noisefrom the pilot signal. The complex conjugate of the filtered pilotsignal and the complex PN despread sequences are multiplied in complexconjugate multiplier 212 b which computes the dot product of the pilotchannel and the PN descrambled sequence to provide a scalar sequence toWalsh sequence multiplier 214 b.

Walsh sequence multiplier 214 b multiplies the input scalar sequencefrom complex conjugate multiplier 212 b by the traffic channel Walshsequence from Walsh generator 218 which is delayed by one PN chipinterval by delay element 216. The multiplied sequence is then providedto combiner means 224.

The second sample is redundantly provided through switch 202 on line 199to demodulator 200 d. The second sample is PN descrambled in PNdescrambling element 204 d. In the exemplary embodiment, PN descramblingelement 204 d descrambles the sample in accordance with two PN sequences(PN_(I) and PN_(Q)) provided by PN generator 206. The PN sequences areprovided directly to PN descrambling element 204 d which results in thesample being demodulated by a PN sequence offset from the sequence usedby demodulator 200 b by one PN chip interval.

The complex PN descrambled sequences are provided to a first input ofcomplex conjugate multiplier 212 d and to pilot filter 210 d. Pilotfilter 210 c uncovers the pilot channel in accordance with the Walshcovering for the pilot channel W_(pilot). In the exemplary embodiment,pilot filter 210 d is simply a low pass filter that removes the noisefrom the pilot signal. The complex conjugate of the filtered pilotsignal and the complex PN despread sequences are multiplied in complexconjugate multiplier 212 d which computes the dot product of the pilotchannel conjugate and the PN descrambled sequence to provide a scalarsequence to Walsh sequence multiplier 214 d.

Walsh sequence multiplier 214 d multiplies the input scalar sequencefrom complex conjugate multiplier 212 d by a Walsh sequence from Walshgenerator 218. The multiplied sequence is then provided to combiner 224.

After the demodulated signals from demodulators 200 b and 200 d havebeen provided to combiner element 224, combiner element 224 combines theenergies and outputs the combined energy values to accumulator 226.Accumulator 226 performs the integration or summation of the inputsymbols over the Walsh symbol interval. Combiner element 224 can performthe combination in a variety of ways. Combiner element 224 could sumonly demodulated data with energy above a threshold value or could sumall of the energies. Alternatively, combiner 224 could select thedemodulated data with the greatest energy. In an alternative embodiment,combiner 224 combines the energy based on the power of the demodulatedpilot from pilot filter 210. For the sake of clarity, optional linesfrom pilot filters 210 to combiner 224 have been omitted.

In FIG. 7, a second fat path demodulator is illustrated where the delaysare applied to the input signal instead of the demodulation elements. InFIG. 7, four demodulators 300 a-300 d are provided to demodulate pathsthat are a fixed half PN chip distance from one another. Thedemodulators move together demodulating PN offsets that are offset fromone another by fixed increments. As described previously amicroprocessor could be used to vary the amount of delay provided bydelay elements 320 and 322. In the exemplary embodiment, one of thedemodulators is the master and tracks the peak of set of multipathsignals and the other demodulators act as slaves and follow the masterdemodulator. In the exemplary embodiment, a metric such as the powerfrom pilot filter 210 can be used by the master finger to track themovement of the peak.

Demodulator 300 a and demodulator 300 c demodulate the received signalthat are delayed with respect to one another by one PN chip interval.The signal provided to input 298 is provided directly to demodulator 300a. The signal is delayed by one PN chip interval by delay element 320prior to being provided to demodulator 300 c. If a first version of thetransmitted signal traverses a first propagation path to be successfullydemodulated by demodulator 300 a, then a second version of thetransmitted signal would need to traverse a second propagation pathrequiring a PN chip interval longer than the time required to traversethe first propagation path in order to be successfully demodulated bydemodulator 300 c.

Half of a PN chip interval later, switch 302 toggles to provide thesample taken half a chip interval later onto line 299. The second sampleis provided directly to demodulator 300 b and delayed by one PN chipinterval by delay element 322 prior to being provided to demodulator 300d. This performs the path diversity combination as described above withrespect to demodulators 300 a and 300 c.

The first sample is provided through switch 302 on line 298 todemodulator 300 a. The sample is PN descrambled in PN descramblingelement 304 a. In the exemplary embodiment, PN descrambling element 204a descrambles the sample in accordance with two PN sequences (PN_(I) andPN_(Q)) provided by PN generator 206. The complex despreading operationis performed as described above with respect to complex despreadingelement 150 a.

The complex PN descrambled sequences are provided to a first input ofcomplex conjugate multiplier 312 a and to pilot filter 310 a. Complexconjugate multiplier removes phase ambiguities that are introduced bythe propagation path. Pilot filter 310 a uncovers the pilot channel inaccordance with the Walsh covering for the pilot channel W_(pilot). Inthe exemplary embodiment, W_(pilot) is the all zeroes Walsh sequence forwhich the uncovering operation is a No Op. In this special case, pilotfilter 310 a is simply a low pass filter which removes the noise fromthe pilot signal. The complex conjugate of the filtered pilot signal andthe complex PN despread sequences are multiplied in complex conjugatemultiplier 312 a which computes the dot product of the pilot channelconjugate and the PN descrambled sequence to provide a scalar sequenceto Walsh sequence multiplier 314 a.

Walsh sequence multiplier 314 a multiplies the input scalar sequencefrom complex conjugate multiplier 312 a by the Walsh traffic sequencefrom Walsh generator 318. The multiplied sequence is then provided tocombiner element 224.

The first sample is redundantly provided through switch 302 on line 298to delay element 320. Delay element 320 delays the signal by one PN chipinterval prior to providing the sample to demodulator 300 c. Thus, thesignal successfully demodulated by demodulator 300 c will have traverseda propagation path that required one PN chip less time to traverse thanthe path that was successfully demodulated by demodulator 300 a. Thesample is PN descrambled in PN descrambling element 304 c. In theexemplary embodiment, PN descrambling element 304 c descrambles thesample in accordance with two PN sequences (PN_(I) and PN_(Q)) providedby PN generator 306.

The complex PN descrambled sequences are provided to a first input ofcomplex conjugate multiplier 312 c and to pilot filter 310 c. Pilotfilter 310 c uncovers the pilot channel in accordance with the Walshcovering for the pilot channel W_(pilot). In the exemplary embodiment,W_(pilot) is the all zeroes Walsh sequence for which the uncoveringoperation is a No Op. In this special case, pilot filter 310 c is simplya low pass filter which removes the noise from the pilot signal. Thecomplex conjugate of the filtered pilot signal and the complex PNdespread sequences are multiplied in complex conjugate multiplier 212 cwhich computes the dot product of the pilot channel conjugate and the PNdescrambled sequence to provide a scalar sequence to Walsh sequencemultiplier 214 c.

Walsh sequence multiplier 314 c multiplies the input scalar sequencefrom complex conjugate multiplier 312 c by the Walsh traffic sequencefrom Walsh generator 318. The multiplied sequence is then provided tocombiner element 324.

After one half PN chip interval, switch 302 toggles so as to put thenext sample, received one half PN chip interval later, on input line 299to demodulators 300 b and 300 d. Within demodulator 300 b, the sample isPN descrambled in PN descrambling element 304 b. In the exemplaryembodiment, PN descrambling element 304 b descrambles the sample inaccordance with two PN sequences (PN_(I) and PN_(Q)) provided by PNgenerator 306 b.

The complex PN descrambled sequences are provided to a first input ofcomplex conjugate multiplier 312 b and to pilot filter 310 b. Pilotfilter 310 b uncovers the pilot channel in accordance with the Walshcovering for the pilot channel W_(pilot). In the exemplary embodiment,pilot filter 310 b is simply a low pass filter which removes the noisefrom the pilot signal. The complex conjugate of the filtered pilotsignal and the complex PN despread sequences are multiplied in complexconjugate multiplier 312 b which computes the dot product of the pilotchannel conjugate and the PN descrambled sequence to provide a scalarsequence to Walsh sequence multiplier 314 b.

Walsh sequence multiplier 314 b multiplies the input scalar sequencefrom complex conjugate multiplier 312 b by the Walsh traffic sequencefrom Walsh generator 318 which is delayed by one PN chip interval bydelay element 316. The multiplied sequence is then provided to combinerelement 324.

The second sample is redundantly provided through switch 302 on line 299to delay element 322. Delay element 322 delays the signal by one PN chipinterval prior to providing it to demodulator 300 d. Demodulator 300 dsuccessfully demodulates a signals that traversed a path that took onePN chip less time to traverse than the path successfully demodulated bydemodulator 300 b. The second sample is PN descrambled in PNdescrambling element 304 d. In the exemplary embodiment, PN descramblingelement 304 d descrambles the sample in accordance with two PN sequences(PN_(I) and PN_(Q)) provided by PN generator 306.

The complex PN descrambled sequences are provided to a first input ofcomplex conjugate multiplier 312 d and to pilot filter 310 d. Pilotfilter 310 d uncovers the pilot channel in accordance with the Walshcovering for the pilot channel W_(pilot). In the exemplary embodiment,pilot filter 310 d is simply a low pass filter that removes the noisefrom the pilot signal. The complex conjugate of the filtered pilotsignal and the complex PN despread sequences are multiplied in complexconjugate multiplier 312 d which computes the dot product of the pilotchannel conjugate and the PN descrambled sequence to provide a scalarsequence to Walsh sequence multiplier 314 d.

Walsh sequence multiplier 314 d multiplies the input scalar sequencefrom complex conjugate multiplier 312 d by the Walsh traffic sequencefrom Walsh generator 318. The multiplied sequence is then provided tocombiner element 324.

After the demodulated signals from demodulators 300 b and 300 d havebeen provided to combiner element 324, combiner element 324 combines theenergies and outputs the combined energy values to accumulator 326. Asdescribed earlier, the combining operation can take many forms all ofwhich are within the scope of the present invention. Accumulator 326performs the integration or summation of the input symbols over theWalsh symbol interval.

Turning to FIG. 8. demodulators 400 a, 400 c and 400 e demodulate thereceived signal delayed with respect to one another by one PN chipinterval. Similarly, demodulators 400 b, 400 d and 400 f demodulate asecond set of samples delayed with respect to one another by one PN chipinterval. The theory behind the operation of the demodulator of FIG. 8is identical to that of FIG. 7. Each demodulator demodulates the signalthat traversed a path that required a time to traverse differing fromone another by one half PN chip interval.

The first sample is provided through switch 402 onto line 398 todemodulator 400 a. The sample is PN descrambled in PN descramblingelement 404 a. In the exemplary embodiment, PN descrambling element 404a descrambles the sample in accordance with two PN sequences (PN_(I) andPN_(Q)) provided by PN generator 406 as described previously.

The complex PN descrambled sequences are provided to a first input ofcomplex conjugate multiplier 412 a and to pilot filter 410 a. Complexconjugate multiplier 412 a removes phase ambiguities that are introducedby the propagation path. Pilot filter 410 a uncovers the pilot channelin accordance with the Walsh covering for the pilot channel W_(pilot).In the exemplary embodiment, W_(pilot) is the all zeroes Walsh sequencefor which the uncovering operation is a No Op. In this special case,pilot filter 410 a is simply a low pass filter which removes the noisefrom the pilot signal. The complex conjugate of the filtered pilotsignal and the complex PN despread sequences are multiplied in complexconjugate multiplier 412 a which computes the dot product of the pilotchannel conjugate and the PN descrambled sequence to provide a scalarsequence to Walsh sequence multiplier 414 a.

Walsh sequence multiplier 414 a multiplies the input scalar sequencefrom complex conjugate multiplier 412 a by the Walsh traffic sequencefrom Walsh generator 418. The multiplied sequence is then provided tocombiner element 424.

The first sample is redundantly provided through switch 402 on line 398to delay element 420. Delay element 420 delays the signal by one PN chipinterval prior to providing the sample to demodulator 400 c. Thus, thesignal successfully demodulated by demodulator 400 c will have traverseda propagation path that required one PN chip less time to traverse thanthe path that was successfully demodulated by demodulator 400 a. Thesample is PN descrambled in PN descrambling element 404 c. In theexemplary embodiment, PN descrambling element 404 c descrambles thesample in accordance with two PN sequences (PN_(I) and PN_(Q)) providedby PN generator 406.

The complex PN descrambled sequences are provided to a first input ofcomplex conjugate multiplier 412 c and to pilot filter 410 c. Pilotfilter 410 c uncovers the pilot channel in accordance with the Walshcovering for the pilot channel W_(pilot). In the exemplary embodiment,W_(pilot) is the all zeroes Walsh sequence for which the uncoveringoperation is a No Op. In this special case, pilot filter 410 c is simplya low pass filter which removes the noise from the pilot signal. Thecomplex conjugate of the filtered pilot signal and the complex PNdespread sequences are multiplied in complex conjugate multiplier 412 cwhich computes the dot product of the pilot channel conjugate and the PNdescrambled sequence to provide a scalar sequence to Walsh sequencemultiplier 414 c.

Walsh sequence multiplier 414 c multiplies the input scalar sequencefrom complex conjugate multiplier 412 c by Walsh traffic sequence fromWalsh generator 418. The multiplied sequence is then provided tocombiner element 424.

The first sample is also redundantly provided through delay element 422a to delay element 422 b. Delay element 422 b delays the signal by oneadditional PN chip interval prior to providing the sample to demodulator400 e. Thus, the signal successfully demodulated by demodulator 400 ewill have traversed a propagation path that required one PN chip lesstime to traverse than the path that was successfully demodulated bydemodulator 400 c and two PN chip intervals less that the signalsuccessfully demodulated by demodulator 400 a. The sample is PNdescrambled in PN descrambling element 404 e. In the exemplaryembodiment, PN descrambling element 404 e descrambles the sample inaccordance with two PN sequences (PN_(I) and PN_(Q)) provided by PNgenerator 406.

The complex PN descrambled sequences are provided to a first input ofcomplex conjugate multiplier 412 e and to pilot filter 410 e. Pilotfilter 410 e uncovers the pilot channel in accordance with the Walshcovering for the pilot channel W_(pilot). In the exemplary embodiment,W_(pilot) is the all zeroes Walsh sequence for which the uncoveringoperation is a No Op. In this special case, pilot filter 410 e is simplya low pass filter which removes the noise from the pilot signal. Thecomplex conjugate of the filtered pilot signal and the complex PNdespread sequences are multiplied in complex conjugate multiplier 412 ewhich computes the dot product of the pilot channel conjugate and the PNdescrambled sequence to provide a scalar sequence to Walsh sequencemultiplier 414 e.

Walsh sequence multiplier 414 e multiplies the input scalar sequencefrom complex conjugate multiplier 412 e by the Walsh traffic sequencefrom Walsh generator 418. The multiplied sequence is then provided tocombiner element 424.

After one half PN chip interval, switch 402 toggles so as to put thenext sample, received one half PN chip interval later, on input line 399to demodulators 400 b, 400 d and 400 f.

Within demodulator 400 b, the sample is PN descrambled in PNdescrambling element 404 b. In the exemplary embodiment, PN descramblingelement 404 b descrambles the sample in accordance with two PN sequences(PN_(I) and PN_(Q)) provided by PN generator 406 b. The complex PNdescrambled sequences are provided to a first input of complex conjugatemultiplier 412 b and to pilot filter 410 b. Pilot filter 410 b uncoversthe pilot channel in accordance with the Walsh covering for the pilotchannel W_(pilot). In the exemplary embodiment, pilot filter 410 b issimply a low pass filter which removes the noise from the pilot signal.The complex conjugate of the filtered pilot signal and the complex PNdespread sequences are multiplied in complex conjugate multiplier 412 bwhich computes the dot product of the pilot channel conjugate and the PNdescrambled sequence to provide a scalar sequence to Walsh sequencemultiplier 414 b.

Walsh sequence multiplier 414 b multiplies the input scalar sequencefrom complex conjugate multiplier 412 b by Walsh traffic sequence fromWalsh generator 418. The multiplied sequence is then provided tocombiner 424.

The second sample is redundantly provided through switch 402 on line 399to delay element 420 a. Delay element 420 a delays the signal by one PNchip interval prior to providing it to demodulator 400 d. Demodulator400 d successfully demodulates a signals that traversed a path that tookone PN chip less time to traverse than the path successfully demodulatedby demodulator 400 b. The second sample is PN descrambled in PNdescrambling element 404 d. In the exemplary embodiment, PN descramblingelement 404 d descrambles the sample in accordance with two PN sequences(PN_(i) and PN_(Q)) provided by PN generator 406.

The complex PN descrambled sequences are provided to a first input ofcomplex conjugate multiplier 412 d and to pilot filter 410 d. Pilotfilter 410 d uncovers the pilot channel in accordance with the Walshcovering for the pilot channel W_(pilot). In the exemplary embodiment,pilot filter 410 d is simply a low pass filter that removes the noisefrom the pilot signal. The complex conjugate of the filtered pilotsignal and the complex PN despread sequences are multiplied in complexconjugate multiplier 412 d which computes the dot product of the pilotchannel conjugate and the PN descrambled sequence to provide a scalarsequence to Walsh sequence multiplier 414 d.

Walsh sequence multiplier 414 d multiplies the input scalar sequencefrom complex conjugate multiplier 412 d by a Walsh sequence from Walshgenerator 418. The multiplied sequence is then provided to combiner 424.

The second sample is redundantly provided through delay element 420 a todelay element 420 b. Delay element 420 b delays the signal by oneadditional PN chip interval prior to providing the sample to demodulator400 f. Thus, the signal successfully demodulated by demodulator 400 fwill have traversed a propagation path that required one PN chip lesstime to traverse than the path that was successfully demodulated bydemodulator 400 d and two PN chip intervals less that the signalsuccessfully demodulated by demodulator 400 b. The sample is PNdescrambled in PN descrambling element 404 f. In the exemplaryembodiment, PN descrambling element 404 f descrambles the sample inaccordance with two PN sequences (PN_(I) and PN_(Q)) provided by PNgenerator 406.

The complex PN descrambled sequences are provided to a first input ofcomplex conjugate multiplier 412 f and to pilot filter 410 f. Pilotfilter 410 f uncovers the pilot channel in accordance with the Walshcovering for the pilot channel W_(pilot). In the exemplary embodiment,W_(pilot) is the all zeroes Walsh sequence for which the uncoveringoperation is a No Op. In this special case, pilot filter 410 f is simplya low pass filter which removes the noise from the pilot signal. Thecomplex conjugate of the filtered pilot signal and the complex PNdespread sequences are multiplied in complex conjugate multiplier 412 fwhich computes the dot product of the pilot channel conjugate and the PNdescrambled sequence to provide a scalar sequence to Walsh sequencemultiplier 414 f.

Walsh sequence multiplier 414 f multiplies the input scalar sequencefrom complex conjugate multiplier 412 f by a Walsh sequence from Walshgenerator 418. The multiplied sequence is then provided to summing means424.

After the demodulated signals from demodulators 400 b, 400 d and 400 fhave been provided to summing element 424, summing element 424 sums theenergies and outputs the summed energy values to accumulator 426.Accumulator 426 performs the integration or summation of the inputsymbols over the Walsh symbol interval.

Turning to FIG. 9, the baseband samples are provide to the fat fingerdemodulator illustrated in FIG. 9 at three times the PN chip rate. Thebaseband samples are provided to switch 502 which switches eachsubsequent sample to a different line. Demodulators 500 a and 500 ddemodulate the received signal that are delayed with respect to oneanother by one PN chip interval. Similarly, demodulators 500 b and 500 edemodulate a second set of samples delayed with respect to one anotherby one PN chip interval. Lastly, demodulator 500 c demodulates a set ofsamples that is unique from those provided to demodulators 500 a, 500 b,500 d and 500 e. The theory behind the operation of the demodulator ofFIG. 9 is identical to that of FIG. 8. Each demodulator demodulates thesignal that traversed a path that required a time to traverse differingfrom one another by one half PN chip interval.

The first sample is provided through switch 502 onto line 499 todemodulator 500 a. The sample is PN descrambled in PN descramblingelement 504 a. In the exemplary embodiment, PN descrambling element 504a descrambles the sample in accordance with two PN sequences (PN_(I) andPN_(Q)) provided by PN generator 506.

The complex PN descrambled sequences are provided to a first input ofcomplex conjugate multiplier 512 a and to pilot filter 510 a. Complexconjugate multiplier 512 a removes phase ambiguities that are introducedby the propagation path. Pilot filter 510 a uncovers the pilot channelin accordance with the Walsh covering for the pilot channel W_(pilot).In the exemplary embodiment, W_(pilot) is the all zeroes Walsh sequencefor which the uncovering operation is a No Op. In this special case,pilot filter 510 a is simply a low pass filter which removes the noisefrom the pilot signal. The complex conjugate of the filtered pilotsignal and the complex PN despread sequences are multiplied in complexconjugate multiplier 512 a which computes the dot product of the pilotchannel conjugate and the PN descrambled sequence to provide a scalarsequence to Walsh sequence multiplier 514 a.

Walsh sequence multiplier 514 a multiplies the input scalar sequencefrom complex conjugate multiplier 512 a by the Walsh traffic sequencefrom Walsh generator 518. The multiplied sequence is then provided tocombiner 524.

The first sample is redundantly provided through switch 502 on line 499to delay element 522. Delay element 522 delays the signal by one PN chipinterval prior to providing the sample to demodulator 500 d. Thus, thesignal successfully demodulated by demodulator 500 d will have traverseda propagation path that required one PN chip less time to traverse thanthe path that was successfully demodulated by demodulator 500 a. Thesample is PN descrambled in PN descrambling element 504 d. In theexemplary embodiment, PN descrambling element 504 d descrambles thesample in accordance with two PN sequences (PN_(I) and PN_(Q)) providedby PN generator 506.

The complex PN descrambled sequences are provided to a first input ofcomplex conjugate multiplier 512 d and to pilot filter 510 d. Pilotfilter 510 c uncovers the pilot channel in accordance with the Walshcovering for the pilot channel W_(pilot). In the exemplary embodiment,W_(pilot) is the all zeroes Walsh sequence for which the uncoveringoperation is a No Op. In this special case, pilot filter 510 d is simplya low pass filter which removes the noise from the pilot signal. Thecomplex conjugate of the filtered pilot signal and the complex PNdespread sequences are multiplied in complex conjugate multiplier 512 dwhich computes the dot product of the pilot channel conjugate and the PNdescrambled sequence to provide a scalar sequence to Walsh sequencemultiplier 514 d.

Walsh sequence multiplier 514 d multiplies the input scalar sequencefrom complex conjugate multiplier 512 d by the Walsh traffic sequencefrom Walsh generator 518. The multiplied sequence is then provided tocombiner 524.

After one third PN chip interval, switch 502 toggles so as to put thenext sample on input line 498 to demodulators 500 b and 500 e.

Within demodulator 500 b, the sample is PN descrambled in PNdescrambling element 504 b. In the exemplary embodiment, PN descramblingelement 504 b descrambles the sample in accordance with two PN sequences(PN_(I) and PN_(Q)) provided by PN generator 506. The complex PNdescrambled sequences are provided to a first input of complex conjugatemultiplier 512 b and to pilot filter 510 b. Pilot filter 510 b uncoversthe pilot channel in accordance with the Walsh covering for the pilotchannel W_(pilot). In the exemplary embodiment, pilot filter 510 b issimply a low pass filter which removes the noise from the pilot signal.The complex conjugate of the filtered pilot signal and the complex PNdespread sequences are multiplied in complex conjugate multiplier 512 bwhich computes the dot product of the pilot channel conjugate and the PNdescrambled sequence to provide a scalar sequence to Walsh sequencemultiplier 514 b.

Walsh sequence multiplier 514 b multiplies the input scalar sequencefrom complex conjugate multiplier 512 b by Walsh traffic sequence fromWalsh generator 518. The multiplied sequence is then provided tocombiner 524.

The second sample is redundantly provided through switch 502 on line 498to delay element 520. Delay element 520 delays the signal by one PN chipinterval prior to providing it to demodulator 500 e. Demodulator 500 esuccessfully demodulates a signals that traversed a path that took onePN chip less time to traverse than the path successfully demodulated bydemodulator 500 b. The second sample is PN descrambled in PNdescrambling element 504 e. In the exemplary embodiment, PN descramblingelement 504 e descrambles the sample in accordance with two PN sequencesPN_(I) and PN_(Q)) provided by PN generator 506.

The complex PN descrambled sequences are provided to a first input ofcomplex conjugate multiplier 512 e and to pilot filter 510 e. Pilotfilter 510 e uncovers the pilot channel in accordance with the Walshcovering for the pilot channel W_(pilot). In the exemplary embodiment,pilot filter 510 e is simply a low pass filter that removes the noisefrom the pilot signal. The complex conjugate of the filtered pilotsignal and the complex PN despread sequences are multiplied in complexconjugate multiplier 512 e which computes the dot product of the pilotchannel conjugate and the PN descrambled sequence to provide a scalarsequence to Walsh sequence multiplier 514 e.

Walsh sequence multiplier 514 e multiplies the input scalar sequencefrom complex conjugate multiplier 512 e by the Walsh traffic sequencefrom Walsh generator 518. The multiplied sequence is then provided tocombiner 524.

One third of a PN chip interval later, switch 502 switches so as toprovide the third base band sample onto output line 497, which providesthe sample directly to demodulator 500 c. The sample is PN descrambledin PN descrambling element 504 c. In the exemplary embodiment, PNdescrambling element 504 c descrambles the sample in accordance with twoPN sequences (PN_(I) and PN_(Q)) provided by PN generator 506.

The complex PN descrambled sequences are provided to a first input ofcomplex conjugate multiplier 512 c and to pilot filter 510 c. Pilotfilter 510 c uncovers the pilot channel in accordance with the Walshcovering for the pilot channel W_(pilot). In the exemplary embodiment,W_(pilot) is the all zeroes Walsh sequence for which the uncoveringoperation is a No Op. In this special case, pilot filter 510 c is simplya low pass filter which removes the noise from the pilot signal. Thecomplex conjugate of the filtered pilot signal and the complex PNdespread sequences are multiplied in complex conjugate multiplier 512 cwhich computes the dot product of the pilot channel conjugate and the PNdescrambled sequence to provide a scalar sequence to Walsh sequencemultiplier 514 c.

Walsh sequence multiplier 514 c multiplies the input scalar sequencefrom complex conjugate multiplier 512 c by the Walsh traffic sequencefrom Walsh generator 518 and provides the result to combiner 524combines the energies of the demodulated signals from demodulators 500a, 500 b, 500 c, 500 d and 500 e and provides the result to accumulator526. As described previously there are many alternative methods ofcombining the demodulated data all of which are within the scope of thepresent invention. Accumulator 526 accumulates the combined energyvalues over the Walsh symbol interval and outputs the result.

FIG. 10 illustrates a modification to FIG. 7 which is applicable to allof the previous embodiments illustrated in FIGS. 6, 7, 8 and 9. FIG. 10illustrates a modification to FIG. 7 which allows for the elimination ofswitch 302. In FIG. 10, four demodulators 600 a, 600 b, 600 c and 600 dare provided to demodulate paths that are a fixed half PN chip distancefrom one another. The received samples are provided at twice the PN chiprate to demodulators 600 a, 600 b, 600 c and 600 d. Pilot filters 610 aand 610 c ignore the even samples and pilot filters 610 b and 610 dignore the odd samples. Combiner 624 only combines demodulated oddsamples from demodulators 600 a and 600 c with demodulated even samplesfrom demodulators 600 b and 600 d.

The first sample is provided directly to demodulators 600 aand 600 b andis delayed by one PN chip interval by delay elements 620 and 622 beforebeing provided to demodulators 600 c and 600 d, respectively. The sampleis PN descrambled in PN descrambling elements 604 a, 604 b, 604 c and604 d. In the exemplary embodiment, PN descrambling elements 604 a, 604b, 604 c and 604 d descramble the sample in accordance with two PNsequences (PN_(I) and PN_(Q)) provided by PN generator 606. The complexdescrambling operation is performed as described above with respect tocomplex despreading element 150 a.

The complex PN descrambled sequences are provided to a first input ofcomplex conjugate multiplier 612 a, 612 b, 612 c and 612 d and to pilotfilter 610 a, 610 b, 610 c and 610 d. Complex conjugate multiplierremoves phase ambiguities that are introduced by the propagation path.Pilot filters 610 b and 610 d ignore the first sample and all future oddsamples. Pilot filters 610 a and 610 c uncover the pilot channel inaccordance with the Walsh covering for the pilot channel W_(pilot). Inthe exemplary embodiment, W_(pilot) is the all zeroes Walsh sequence forwhich the uncovering operation is a No Op. In this special case, pilotfilter 610 a and 610 c are simply low pass filters which remove thenoise from the pilot signal. The complex conjugate of the filtered pilotsignal and the complex PN despread sequences are multiplied in complexconjugate multipliers 612 a and 612 c which compute the dot product ofthe pilot channel conjugate and the PN descrambled sequence to providescalar sequences to Walsh sequence multipliers 614 a and 614 c.

Walsh sequence multipliers 614 a and 614 c multiply the input scalarsequence from complex conjugate multipliers 612 a and 612 c by the Walshtraffic sequence from Walsh generator 618. The multiplied sequence isthen provided to combiner element 624. Note that although PNdescrambling and Walsh multiplication are provided on the first sampleby demodulators 600 b and 600 d, combiner 624 ignores the data providedfrom demodulators 600 b and 600 d for odd samples as erroneous.

The second sample is, then, provided directly to demodulators 600 a and600 b and is delayed by one PN chip interval by delay elements 620 and622 before being provided to demodulators 600 c and 600 d, respectively.The sample is PN descrambled in PN descrambling elements 604 a, 604 b,604 c and 604 d. In the exemplary embodiment, PN descrambling elements604 a, 604 b, 604 c and 604 d descramble the sample in accordance withtwo PN sequences PN_(I) and PN_(Q)) provided by PN generator 606. Thecomplex descrambling operation is performed as described above withrespect to complex despreading element 150 a.

The complex PN descrambled sequences are provided to a first input ofcomplex conjugate multiplier 612 a, 612 b, 612 c and 612 d and to pilotfilter 610 a, 610 b, 610 c and 610 d. Complex conjugate multipliersremove phase ambiguities that are introduced by the propagation path.Pilot filters 610 a and 610 c ignore the second sample and all futureeven samples. Pilot filters 610 b and 610 d uncover the pilot channel inaccordance with the Walsh covering for the pilot channel W_(pilot). Inthe exemplary embodiment, W_(pilot) is the all zeroes Walsh sequence forwhich the uncovering operation is a No Op. In this special case, pilotfilter 610 b and 610 d are simply low pass filters which remove thenoise from the pilot signal. The complex conjugate of the filtered pilotsignal and the complex PN despread sequences are multiplied in complexconjugate multipliers 612 b and 612 d which compute the dot product ofthe pilot channel conjugate and the PN descrambled sequence to providescalar sequences to Walsh sequence multipliers 614 b and 614 d.

Walsh sequence multipliers 614 b and 614 d multiply the input scalarsequence from complex conjugate multiplier 612 b and 612 d by the Walshtraffic sequence from Walsh generator 618. The multiplied sequence isthen provided to combiner element 624. Note that although PNdescrambling and Walsh multiplication are provided on the second sampleby demodulators 600 a and 600 c, combiner 624 ignores the data providedfrom demodulators 600 b and 600 d for odd samples as erroneous.

After the demodulated signals from demodulators 600 b and 600 d havebeen provided to combiner element 624, combiner element 624 combines theenergies and outputs the combined energy values to accumulator 626. Asdescribed earlier, the combining operation can take many forms all ofwhich are within the scope of the present invention. Accumulator 626performs the integration or summation of the input symbols over theWalsh symbol interval.

FIG. 11 illustrates a modification to FIG. 10 which is applicable to allof the previous embodiments illustrated in FIGS. 6, 7, 8 and 9. FIG. 11illustrates a modification to FIG. 10 which allows for the eliminationof all but one Walsh multiplier. In FIG. 10, four demodulators 650 a,650 b, 650 c and 650 d are provided to demodulate paths that are a fixedhalf PN chip distance from one another. The received samples areprovided at twice the PN chip rate to demodulators 650 a, 650 b, 650 cand 650 d. Pilot filters 660 a and 660 c ignore the even samples andpilot filters 660 b and 660 d ignore the odd samples. Combiner 674 onlycombines demodulated odd samples from demodulators 650 a and 650 c withdemodulated even samples from demodulators 650 b and 650 d.

The first sample is provided directly to demodulators 650 a and 650 band is delayed by one PN chip interval by delay elements 670 and 672before being provided to demodulators 650 c and 650 d, respectively. Thesample is PN descrambled in PN descrambling elements 654 a, 654 b, 654 cand 654 d. In the exemplary embodiment, PN descrambling elements 654 a,654 b, 654 c and 654 d descramble the sample in accordance with two PNsequences (PN_(I) and PN_(Q)) provided by PN generator 656.

The complex PN descrambled sequences are provided to a first input ofcomplex conjugate multipliers 662 a, 662 b, 662 c and 662 d and to pilotfilters 660 a, 660 b, 660 c and 660 d. Complex conjugate multipliersremove phase ambiguities that are introduced by the propagation path.Pilot filters 660 b and 660 d ignore the first sample and all future oddsamples. Pilot filters 660 a and 660 c uncover the pilot channel inaccordance with the Walsh covering for the pilot channel W_(pilot). Inthe exemplary embodiment, W_(pilot) is the all zeroes Walsh sequence forwhich the uncovering operation is a No Op. In this special case, pilotfilter 660 a and 660 c are simply low pass filters which remove thenoise from the pilot signal.

The complex conjugate of the filtered pilot signal and the complex PNdespread sequences are multiplied in complex conjugate multipliers 662 aand 662 c which compute the dot product of the pilot channel conjugateand the PN descrambled sequence to provide scalar sequences to combiner674. Note that although PN descrambling and Walsh multiplication areprovided on the first sample by demodulators 650 b and 650 d, combiner674 ignores the data provided from demodulators 650 b and 650 d for oddsamples as erroneous.

The second sample is, then, provided directly to demodulators 650 a and650 b and is delayed by one PN chip interval by delay elements 620 and622 before being provided to demodulators 650 c and 650 d, respectively.The sample is PN descrambled in PN descrambling elements 654 a, 654 b,654 c and 654 d. In the exemplary embodiment, PN descrambling elements654 a, 654 b, 654 c and 654 d descramble the sample in accordance withtwo PN sequences (PN_(I) and PN_(Q)) provided by PN generator 656. Thecomplex descrambling operation is performed as described above withrespect to complex despreading element 150 a.

The complex PN descrambled sequences are provided to a first input ofcomplex conjugate multipliers 662 a, 662 b, 662 c and 662 d and to pilotfilters 660 a, 660 b, 660 c and 660 d. Complex conjugate multipliersremove phase ambiguities that are introduced by the propagation path.Pilot filters 660 a and 660 c ignore the second sample and all futureeven samples.

Pilot filters 660 b and 660 d uncover the pilot channel in accordancewith the Walsh covering for the pilot channel W_(pilot). In theexemplary embodiment, W_(pilot) is the all zeroes Walsh sequence forwhich the uncovering operation is a No Op. In this special case, pilotfilters 660 b and 660 d are simply low pass filters which removes thenoise from the pilot signal. The complex conjugate of the filtered pilotsignal and the complex PN despread sequences are multiplied in complexconjugate multiplier 662 b and 662 d which compute the dot product ofthe pilot channel conjugate and the PN descrambled sequence to providescalar sequences to combiner 674.

Combiner 674 combines the odd samples demodulated by demodulators 650 aand 650 c with the even samples demodulated by demodulators 650 b and650 d. Combiner 674 can take many forms as discussed previously withrespect to the previous combiners. The combined symbols are thenprovided to Walsh sequence multiplier 664.

Walsh sequence multiplier 664 multiplies the combined symbol sequence bythe Walsh traffic sequence W_(Traffic) which is provided by Walshsequence generator 668. The output from Walsh sequence multiplier 664 isprovided to accumulator 676. Accumulator 676 accumulates the Walshmultiplied sequence to provide Walsh despread data.

FIG. 12 illustrates a modification to FIG. 7 which is equally applicableto the modification of FIGS. 6, 7, 8 and 9. FIG. 12 provides for thedemodulation of four paths that are one half PN chip apart using twodemodulators. Demodulator 700 a demodulates two paths that are one halfPN chip apart and Demodulator 700 b demodulates two additional pathsthat are one half PN chip apart from one another and one full PN chipfrom the paths demodulated by demodulator 700 a.

The samples are provided at twice the PN chip rate. The samples areprovided directly to demodulator 700 a and are delayed by one PN chipprior to being provided to demodulator 700 b. The sample is PNdescrambled in PN descrambling elements 704 a and 704 b. In theexemplary embodiment, PN descrambling elements 704 a and 704 bdescramble the sample in accordance with two PN sequences (PN_(I) andPN_(Q)) provided by PN generator 706. The complex descrambling operationis performed as described above with respect to complex despreadingelement 150 a.

The complex PN descrambled sequences are provided to a first input ofcomplex conjugate multiplier 712 a and 712 b and to pilot filter 710 aand 710 b. Complex conjugate multipliers remove phase ambiguities thatare introduced by the propagation path.

In the first embodiment of pilot filters 710 a and 710 b, pilot filters710 a and 710 b consist of two independent filters. A first of the twoindependent filters processes the odd samples and a second of the twoindependent filters processes the even samples.

In this embodiment, a first sample is provided to pilot filter 710 a and710 b, and is processed by the independent filter within it whichprocesses the odd samples. The output of the pilot filters 710 a and 710b are provided to complex conjugate multipliers 712 a and 712 b whichmultiply the conjugate of the pilot filter output with the descrambledsignal from PN descrambling element 704 a and 704 b. Note the odddescrambled symbols are complex multiplied by the odd pilot symbols.

In this embodiment, a second sample is provided to pilot filter 710 aand 710 b, and is processed by the independent filter within it whichprocesses the even samples. The output of the pilot filters 710 a and710 b are provided to complex conjugate multipliers 712 a and 712 bwhich multiply the conjugate of the pilot filter output with thedescrambled signal from PN descrambling element 704 a and 704 b. Notethe even descrambled symbols are complex multiplied by the even pilotsymbols.

In a second embodiment of pilot filters 710 a and 710 b, each pilotfilter simply processes all of the samples.

The data from complex conjugate multipliers 712 a and 712 b are providedto Walsh sequence multipliers 714 a and 714 b. The Walsh trafficsequence is provided by Walsh generator 718 and the product sequence isprovided from Walsh sequence multipliers 714 a and 714 b to combiner724. Combiner 724 combines the Walsh sequence multiplied data asdescribed with respect to combiner 224. The combined symbols areprovided to accumulator 726 which accumulates the energy over the Walshsymbol length.

FIG. 13 illustrates a modification to FIG. 12. FIG. 13 essentiallyperforms the operation as described with respect to FIG. 12 using thesecond implementation of the pilot filter. Demodulator 800 a demodulatestwo paths that are one half PN chip apart and demodulator 800 bdemodulates two additional paths that are one half PN chip apart fromone another and one full PN chip from the paths demodulated bydemodulator 800 a.

The samples are provided at twice the PN chip rate. The samples areprovided to sample combiners 834 a and 834 b. Sample combiners 834 a and834 b receive the samples at twice the PN chip rate and sum togethersample received one half PN chip apart and provide the sum todemodulators 800 a and 800 b at the chip rate.

The first sample is provided to sample combiners 834 and is providedthrough switches 832 to delay elements 828. Delay elements 828 delay thesample by one half PN chip interval before providing the sample to afirst summing input of summers 830. The second sample is then providedto equalizers 834 and provided through switches 832 to a second summinginput of summer 830.

The two samples are summed together by summers 830 and the output isprovided by sample combiner 834 a to demodulator 800 a and by samplecombiners 834 b to delay element 822. Delay element 822 delays theresult from summer 830 b by one PN chip interval before providing it todemodulator 800 b.

In demodulators 800 a and 800 b, the received summed samples areprovided to PN descrambling elements 804 a and 804 b. In the exemplaryembodiment, PN descrambling elements 804 a and 804 b descramble thesample in accordance with two PN sequences (PN_(I) and PN_(Q)) providedby PN generator 806. The complex descrambling operation is performed asdescribed above with respect to complex despreading element 150 a.

The complex PN descrambled sequences are provided to a first input ofcomplex conjugate multipliers 812 a and 812 b and to pilot filters 810 aand 810 b. Complex conjugate multipliers remove phase ambiguities thatare introduced by the propagation path. Complex conjugate multipliers812 a and 812 b multiply the PN descramble symbols by the conjugate ofthe pilot filter symbols.

The data from complex conjugate multipliers 812 a and 812 b are providedto Walsh sequence multipliers 814 a and 814 b. The Walsh trafficsequence is provided by Walsh generator 818 and the product sequence isprovided from Walsh sequence multipliers 814 a and 814 b to combiner824. Combiner 824 combines the Walsh sequence multiplied data asdescribed with respect to combiner 224. The combined symbols areprovided to accumulator 826 which accumulates the energy over the Walshsymbol length. Although the present invention is described with respectto traditional PN sequences such as those in IS-95, the presentinvention is equally applicable to other spreading sequences such asGold codes. Moreover, although coherent detection using pilot channeloffer significant benefits in system performance, the present inventionis equally applicable to non coherent detection methods that do not usea pilot channel.

The previous description of the preferred embodiments is provided toenable any person skilled in the art to make or use the presentinvention. The various modifications to these embodiments will bereadily apparent to those skilled in the art, and the generic principlesdefined herein may be applied to other embodiments without the use ofthe inventive faculty. Thus, the present invention is not intended to belimited to the embodiments shown herein but is to be accorded the widestscope consistent with the principles and novel features disclosedherein.

We claim:
 1. A spread spectrum receiver for receiving multiple spreadspectrum signals each traveling upon a different propagation path andeach having a resultant arrival time difference with respect to oneanother, said spread spectrum receiver comprising: first demodulatormeans for demodulating a first spread spectrum signal of said multiplespread spectrum signals in accordance with a first arrival time; andsecond demodulator means for demodulating a second spread spectrumsignal of said multiple spread spectrum signals in accordance with afixed time interval difference with respect to said first arrival time,wherein said first demodulator comprises: first pseudonoise descramblingmeans for descrambling said first spread spectrum signal in accordancewith a pseudonoise sequence to provide a first pseudonoise descrambledsignal; first phase adjustment means for filtering a first pilot signalfrom said first pseudonoise descrambled signal to provide a firstfiltered pilot signal and multiplying said first pseudonoise descrambledsignal with said first filtered pilot signal to provide a first phaseadjusted signal; first dechannelization means for multiplying said firstphase adjusted signal by an orthogonal channel sequence; wherein saidspread spectrum receiver further comprises pseudonoise generator forgenerating said pseudonoise sequence and wherein said second demodulatormeans comprises: delay means for receiving said pseudonoise sequence andfor delaying said pseudonoise sequence by said fixed time intervaldifference to provide a delayed pseudonoise sequence; second pseudonoisedescrambling means for descrambling said second spread spectrum signalin accordance with said delayed pseudonoise sequence to provide a secondpseudonoise descrambled signal; second phase adjustment means forfiltering a second pilot signal to provide a second filtered pilotsignal from said second pseudonoise descrambled signal and multiplyingsaid second pseudonoise descrambled signal with said second filteredpilot signal to provide a second phase adjusted signal; and seconddechannelization means for multiplying said second phase adjusted signalby a delayed orthogonal channel sequence.
 2. The spread spectrumreceiver of claim 1 wherein said second demodulator means comprises:delay means for receiving said first spread spectrum signal and fordelaying said first spread spectrum signal by said fixed time intervaldifference to provide said second spread spectrum signal; secondpseudonoise descrambling means for descrambling said second spreadspectrum signal in accordance with said pseudonoise sequence to providea second pseudonoise descrambled signal; second phase adjustment meansfor filtering a second pilot signal from said second pseudonoisedescrambled signal to provide a second filtered pilot signal andmultiplying said second pseudonoise descrambled signal with said secondfiltered pilot signal to provide a second phase adjusted signal; andsecond dechannelization means for multiplying said second phase adjustedsignal by a second orthogonal channel sequence.
 3. The spread spectrumreceiver of claim 1 further comprising a combiner means for receivingsaid first demodulated spread spectrum signal and said seconddemodulated spread spectrum signal and for combining said firstdemodulated spread spectrum signal and said second demodulated spreadspectrum signal.
 4. The spread spectrum receiver of claim 1 furthercomprising Walsh sequence generator means for generating said orthogonalchannel sequence and wherein said spread spectrum receiver furthercomprises: delay element for receiving said orthogonal channel sequenceand for delaying said orthogonal channel sequence by said fixed timeinterval difference to provide said delayed orthogonal channel sequence.5. The spread spectrum receiver of claim 1 further comprising switchingmeans for providing said first spread spectrum signal to said firstdemodulator means and for switching after said fixed time intervaldifference to provide said second spread spectrum signal to said seconddemodulator means.
 6. The spread spectrum receiver of claim 1 whereinsaid first phase adjustment means comprises: complex conjugatemultiplier means for receiving said first pseudonoise descrambled signaland said first filtered pilot signal and for multiplying said firstpseudonoise descrambled signal with said first filtered pilot signal. 7.The spread spectrum receiver of claim 6 wherein a pilot filter extractssaid first filtered pilot signal in accordance with an orthogonal pilotsequence.
 8. A method for receiving multiple spread spectrum signalseach traveling upon a different propagation path and each having aresultant arrival time difference with respect to one another, saidmethod comprising: demodulating a first spread spectrum signal of saidmultiple spread spectrum signals in accordance with a first arrivaltime; demodulating a second spread spectrum signal of said multiplespread spectrum signals in accordance with a fixed time intervaldifference with respect to said first arrival time, wherein saiddemodulating said first spread spectrum signal comprises: descramblingsaid first spread spectrum signal in accordance with a pseudonoisesequence to provide a first pseudonoise descrambled signal; filtering afirst pilot signal from said first pseudonoise descrambled signal toprovide a first filtered pilot signal; multiplying said firstpseudonoise descrambled signal with said first filtered pilot signal toprovide a first phase adjusted signal; multiplying said first phaseadjusted signal by an orthogonal channel sequence; generating saidpseudonoise sequence; delaying said pseudonoise sequence by said fixedtime interval difference to provide a delayed pseudonoise sequence;descrambling said first spread spectrum signal in accordance with saiddelayed pseudonoise sequence to provide a second pseudonoise descrambledsignal; filtering a second pilot signal from said second pseudonoisedescrambled signal to provide a second filtered pilot signal andmultiplying said second pseudonoise descrambled signal with said secondfiltered pilot signal to provide a second phase adjusted signal; andmultiplying said second phase adjusted signal by an orthogonal channelsequence.
 9. The method of claim 8 wherein said demodulating said secondspread spectrum signal comprises: delaying said first spread spectrumsignal by said fixed time interval difference to provide said secondspread spectrum signal; descrambling said second spread spectrum signalin accordance with said pseudonoise sequence to provide a secondpseudonoise descrambled signal; filtering a second pilot signal fromsaid second pseudonoise descrambled signal to provide a second filteredpilot signal and multiplying said second pseudonoise descrambled signalwith said second filtered pilot signal to provide a second phaseadjusted signal; and multiplying said second phase adjusted signal by asecond orthogonal channel sequence.
 10. The method of claim 8 furthercomprising combining said first demodulated spread spectrum signal andsaid second demodulated spread spectrum signal.
 11. A method forreceiving multiple spread spectrum signals each traveling upon adifferent propagation path and each having a resultant arrival timedifference with respect to one another, said method comprising:demodulating a first spread spectrum signal of said multiple spreadspectrum signals in accordance with a first arrival time; anddemodulating a second spread spectrum signal of said multiple spreadspectrum signals in accordance with a fixed time interval differencewith respect to said first arrival time, wherein said demodulating saidfirst spread spectrum signal comprises: descrambling said first spreadspectrum signal in accordance with a pseudonoise sequence to provide afirst pseudonoise descrambled signal; filtering a first pilot signalfrom said first pseudonoise descrambled signal to provide a firstfiltered pilot signal; multiplying said first pseudonoise descrambledsignal with said first filtered pilot signal to provide a first phaseadjusted signal; multiplying said first phase adjusted signal by anorthogonal channel sequence; generating said orthogonal channelsequence; and delaying said orthogonal channel sequence by said fixedtime interval difference.
 12. The method of claim 11 further comprising:first switching to provide said first spread spectrum signal; and secondswitching after said fixed time interval difference to provide saidsecond spread spectrum signal.